(1) Field of the Invention
The present invention relates to a method for producing a grafted ethylene-acrylic acid ester copolymer obtained by grafting a specifically limited block copolymer onto an ethylene-acrylic acid ester copolymer, and more particularly relates to a method for producing a grafted ethylene-acrylic acid ester copolymer in a simple manner and in a high graft efficiency.
(2) Related Art Statement
Ethylene-acrylic acid ester copolymer is flexible over a wide temperature range and has a high heat resistance, and therefore the copolymer is used in the form of a foamed article or is used as electric parts. Particularly, it has recently been investigated to use a blend of an ethylene-acrylic acid ester copolymer with, for example, polyphenylene ether, as an improver of shock resistance of engineering plastics.
In order to produce a homogeneous blend of ethylene-acrylic acid ester copolymer with engineering plastics, particularly polyphenylene ether, there has been attempted to graft styrene onto an olefin (co)polymer. For example, Japanese Patent Application Laid-open Specification No. 226,042/84 discloses a method, wherein polystyrene is grafted onto an olefin (co)polymer in the presence of an organic peroxide under a melted state; and Japanese Patent Laid-open Specification No. 185,309/82 discloses a method, wherein an olefin (co)polymer is impregnated with styrene monomer, and the impregnated styrene monomer is polymerized, whereby polystyrene is grafted onto the olefin (co)polymer. However, in the former method, ethylene-acrylic acid ester copolymer is essentially incompatible with polystyrene, and the grafting reaction hardly occurs, and hence the layers formed of ethylene-acrylic acid ester copolymer segments separate from layers formed of polystyrene segments. In the latter method, a polymerization reaction is carried out, and therefore complicated steps are required, and further it is difficult to control the polymerization temperature and the molecular weight of the impregnated ethylene-acrylic acid ester copolymer in the commercial production of the grafted ethylene-acrylic acid ester copolymer, and moreover the graft efficiency is poor.
The grafting of polystyrene onto an ethylene-acrylic acid ester copolymer can be carried out by the above described conventional methods. However, the resulting graft copolymer has not satisfactorily excellent properties due to its production method. This is due to the poor dispersion of a polymer, which is different from an ethylene-acrylic acid ester copolymer, into the ethylene-acrylic acid ester copolymer. In order to improve the dispersion of a polymer, which is different from an ethylene-acrylic acid ester copolymer, into the ethylene-acrylic acid ester copolymer, and to make the particle size of the polymer to be dispersed in the ethylene-acrylic acid ester copolymer into a size smaller than a certain value, it is necessary to produce a graft copolymer of an ethylene-acrylic acid ester copolymer with a polymer different from the ethylene-acrylic acid ester copolymer. However, in the above described methods, the yield of the graft copolymer is low, and the above described conventional methods are low in the effect.